1. Field of the Invention
The present invention relates to a magnetic head suspension for supporting a magnetic head slider that reads and/or writes data from and to a recording medium such as a hard disk drive.
2. Related Art
Due to an increase in capacity of a magnetic disk device, a magnetic head suspension is required to enhance a positioning accuracy of a magnetic head slide to a target track. In order to enhance the positioning accuracy, it is required to prevent, as much as possible, vibration of the magnetic head slider when the magnetic head suspension is swung in a seek direction parallel to a disk surface by an actuator such as a voice coil motor.
For example, Japanese Unexamined Patent Publication No. 2005-032393 (hereinafter, referred to as Prior Art Document 1) discloses a magnetic head suspension including a load beam part that has a main body portion in a flat plate shape and paired right and left ribs (flange portions) extending respectively from side edges of the main body portion in a direction opposite from the disk surface. In this magnetic head suspension, the respective side edges of the main body portion are inclined toward a suspension longitudinal center line such that the load beam part is gradually reduced in width as it goes from a proximal end to a distal end in the suspension longitudinal direction. Further, each of the ribs is at least partially curved to form a narrowed portion in a planar view as viewed along a direction perpendicular to the disk surface.
The magnetic head suspension disclosed in Prior Art Document 1 is regarded such that the provision of the narrowed portions reduces the weight of the load beam part, thereby allowing the resonant frequency of the load beam part to be higher than the conventional configurations.
As described above, Prior Art Document 1 discloses the feature that the resonant frequency can be raised by the narrowed portions provided to the flange portions of the load beam part. However, it is unknown in Prior Art Document 1 which one of various vibration modes is focused on with regard to the resonant frequency possibly generated to a magnetic head suspension.
Japanese Unexamined Patent Publication No. 2008-021374 (hereinafter, referred to as Prior Art Document 2) discloses a magnetic head suspension including first and second members. The first member includes an elastic deformation portion and a main body portion that extends forward from the elastic deformation portion. The main body portion is gradually reduced in width as it advances forward and is provided with flanges at right and left side edges thereof. The second member is substantially in a T-letter shape that includes a wide portion provided at a proximal edge with a flange and a narrow portion extending forward from the wide portion. The narrow portion has a width smaller than that of the main body portion, and is provided at right and left side edges with flanges.
In Prior Art Document 2, the first and second members are joined with each other to form an assembly, which integrally configures a load bending part and a load beam part.
That is, the elastic deformation portion configures the load bending part, and the main body portion and the second member configure the load beam part.
More specifically, the side edges of the main body portion are provided with the flanges and are inclined so as to be gradually come closer to the suspension longitudinal center line as they advance to the respective front ends. The side edges of the narrow portion are provided with the flanges and extend substantially in parallel with the suspension longitudinal center line at positions closer to the center line than the side edges of the main body portion.
Accordingly, the load beam part configured by the main body portion and the second member has the right and left side edges that are provided with the flanges substantially in the entire areas in the suspension longitudinal direction. The side edges have proximal end regions that are respectively inclined at a first inclination angle with respect to the center line so as to gradually come closer to the center line as they advance to the respective front ends, and distal end regions that extend substantially in parallel with the center line.
In the magnetic head suspension disclosed in Prior Art Document 2, the distal end region of the load beam part is configured by the narrow portion, thereby successfully reducing the width of the load beam part as compared to the conventional cases. This will lead to the reduction of the moment of inertia of the load beam part about a twist center line along the center line so as to raise the resonant frequency in a first torsion mode.
Out of the various vibration modes possibly generated in the magnetic head suspension, the first and second torsion modes have the resonance frequencies within the low frequency range.
Accordingly, in order to enhance the positioning accuracy of the magnetic head slider, it is required to prevent the displacement of the magnetic head slider due to the resonant vibrations in the first and second torsion modes.
The magnetic head suspension disclosed by Prior Art Document 2 is regarded such that the resonant vibration in the first torsion mode can be prevented by the increased resonant frequency in the first torsion mode. However, in the magnetic head suspension, the second torsion mode is not taken into consideration.
The amount (gain) of displacement of the magnetic head slider due to the resonant vibration in the first torsion mode can be easily reduced by adjusting a bended position of the load bending part. However, it is extremely difficult to reduce the amount (gain) of displacement of the magnetic head slider due to the resonant vibration in the second torsion mode by adjusting the bended position of the load bending part.
More specifically, in the resonant vibration in the first torsion mode, in a state where a position at which the load bending part is arranged and a position at which a dimple of the load beam part is arranged are fixed so as not to be displaced in a z direction perpendicular to the disk surface (namely, the positions form nodes), only the load beam part is principally twisted about a twist center line along the suspension longitudinal center line so that a substantially center portion between the two nodes in the suspension longitudinal direction is displaced to the maximum in the z direction (namely, the substantially center portion forms an antinode).
On the other hand, in the resonant vibration in the second torsion mode, in a state where three positions form the nodes, the three positions including a position at which a supporting part is rigidly fixed with respect to the z direction (in a case where the supporting part is configured by a base plate, a position of a boss portion that is fixed by caulking (or swaging) to a carriage arm coupled to an actuator; hereinafter, referred to as a supporting part fixed position), a position at which the dimple is arranged, and a halfway position of the load beam part that is located at a substantially center in the suspension longitudinal direction between the supporting part fixed position and the position of the dimple, a distal end region of the supporting part, the load bending part and the load beam part are twisted about the twist center line along the suspension longitudinal center line so that two portions form the antinode, the two portions including a substantially center portion between the supporting part fixed position and the halfway position of the load beam part in the suspension longitudinal direction and a substantially center portion between the halfway position of the load beam part and the position of the dimple in the suspension longitudinal direction.
As explained above, in the resonant vibration in the second torsion mode, the node is generated in the halfway position of the load beam part in the suspension longitudinal direction. The load beam part includes the main body portion substantially parallel to the disk surface, and the paired right and left flange portions extending respectively from the right and left side edges of the main body portion in the direction opposite from the disk surface. That is, in the resonant vibration in the second torsion mode, the node is generated in an area having a high rigidity with respect to the twist motion about the twist center line along the longitudinal center line.
For this reason, the resonant frequencies in the second torsion mode are likely to be varied among the individual suspensions. Accordingly, reduction of the gain of the magnetic head slider in the resonant vibration in the second torsion mode by adjusting the bended position of the load bending part is much more difficult than reduction of the gain of the magnetic head slider in the resonant vibration in the first torsion mode.